1. Field of the Invention
The present invention generally relates to speech recognition control systems. More particularly, the present invention relates to a hands-free voice command automatic dialing system especially suited for use in a noisy environment such as encountered in vehicular radiotelephone applications.
2. Description of the Prior Art
Typically, in both radio and landline telephone systems, the user communicates by means of a handset that includes a speaker at one end, which is placed close to the user's ear, and a microphone at the other end, which is held close to the user's mouth. In operation, one hand of the user is occupied holding the handset in its proper orientation, thereby leaving the user's only free hand to accomplish tasks such as driving a vehicle. In order to provide a greater degree of freedom for the user, speakerphones have commonly been used in landline telephone systems. Recently, vehicular speakerphones have been developed for use in automobiles. For example, U.S. Pat. Nos. 4,378,603 by Eastmond and 4,400,584 by Vilmur, both assigned to the same assignee as the present invention, describe vehicular speakerphones with hands-free operation.
Speech recognition control systems, which are responsive to human voice, are highly desirable for use in automotive applications. Most mobile radio transceiver functions (e.g., on/off, transmit/receive, volume, squelch, etc.) or mobile radiotelephone control functions (e.g., pushbutton dialing, speech recognizer training, telephone call answering) may readily be achieved by voice command without requiring any manual operations. Hence, the use of speech recognition with a vehicular speakerphone has the potential for providing a totally hands-free telephone conversation without ever requiring the automobile driver to remove his hands from the steering wheel or take his eyes off the road. This feature has not only extended the hands-free capability of speakerphones, but also has added to the safety and convenience of using mobile radiotelephones in vehicles.
Unfortunately, the application of complete hands-free control to a mobile radiotelephone introduces several significant obstacles When speech recognition is utilized in a vehicular environment, the high degree of ambient noise inherent in a vehicle presents a considerable obstacle to reliable voice control. Furthermore, a vehicular speakerphone typically has a microphone that is distant from the user's mouth, such as being mounted overhead on the automobile sun visor. Consequently, the required high microphone sensitivity causes a large increase in the amount of environmental background noise being applied to the speech recognizer, which degrades its recognition reliability.
More particularly, the problem of speech recognition errors in an automatic dialing telephone considerably inhibits the performance of the system. The features of automatic and repertory dialing have recently been utilized in cellular telephone applications, such that the user can verbally enter telephone digits or verbally recall prestored numbers with predefined keywords. If the speech recognition unit erroneously recognizes a command keyword, the voice command controller will generally reply the command recognized to the user for verification purposes. The user would then re-enter the correct keyword. This entry/verification/re-entry process is usually only a minor inconvenience, since it typically takes only a few seconds for the majority of commands. However, if the speech recognizer erroneously detects a single digit in a lengthy sequence of digits representing a telephone number, the entry/verification/re-entry process becomes tremendously time consuming and, at the very least, considerably frustrating to the user.
For these reasons, the prior art techniques for entering digits by voice command have been severely limited. Some voice recognition controllers wait for the user to utter a predetermined number of digits, e.g., seven or eleven for a telephone number. Upon recognition of the last expected digit, the controller utilizes speech synthesis to verbally reply the number recognized to the user for verification. The user can then prevent entry of an erroneously recognized telephone number by speaking a predetermined error command keyword. However, in vehicular environments where the recognition accuracy is not high, it may take several repetitions of the entire digit sequence for correct recognition. In other versions, the voice command dialer will repeat every single digit immediately after recognition. Although this alternative may prove more reliable in a high noise environment, it needlessly requires a considerable amount of time to enter a lengthy string of digits, especially when the recognition accuracy is high. Moreover, the single digit verification process is very annoying when a digit is incorrectly recognized, since the user can easily forget the next digit to be entered when he must mentally stop to say an error command, repeat the incorrect single digit, listen to the corrected reply, and then continue. On the whole, the prior art digit entry/verification procedures have not been user-friendly.
A need, therefore, exists for an intelligent method for entering and verifying a sequence of digits by voice command in a speech recognition control system.